The present invention generally relates to manufacturing processes and equipment using masks and masking structures and, more particularly, to a system and method for managing reticles and reticle stocking locations as part of an entire semiconductor processing system.
A conventional semiconductor fabrication plant typically includes multiple fabrication areas or bays interconnected by a path, such as a conveyor belt. Each bay generally includes the requisite fabrication tools (interconnected by a subpath) to process semiconductor wafers for a particular purpose, such as photolithography, chemical-mechanical polishing, or chemical vapor deposition. Material stockers or stocking tools generally are located about the plant and store semiconductor wafers waiting to be processed. The wafers are typically stored in containers, such as cassettes, each of which can hold up to 25 wafers. The cassettes are then stored in carriers that facilitate movement throughout the plant. The carriers can move material in lots, primarily between stocking locations, such as production wafers, test wafers, or empty cassettes to ensure that the process is moving smoothly.
Integrated into the wafer processing line is a photolithography process that occupies a substantial amount of floor space and involves a high level of capital investment to maintain. A wafer is subjected to a photolithography process of some type and usually involves applying a layer of photoresist material, such as silicon dioxide, over the surface of a wafer using a coating machine. The wafer is then moved to an exposure tool, such as a photolithography stepper that exposes the photoresist layer to a patterned light source. The light source is patterned using a mask structure or a reticle. The reticle contains clear and opaque features that generally define the pattern to be created in the photoresist layer. The exposed photoresist is then developed and regions of the photoresist are dissolved leaving a pattern on the photoresist layer. The exposed portions of the underlying wafer are then subjected to further processing.
Depending on the type of IC device being manufactured, the wafer may be subjected to the photolithography process several times as layers are formed successively over prior layers to ultimately form the semiconductor device. To perform the various photolithography processes, a semiconductor plant has a photolithography area that has a number of steppers that utilize an entire cataloged library of reticles. The number of reticles that need to be readily available can easily exceed one thousand, due to the number of different products that can be manufactured in one facility, with each reticle having a replacement cost of about $1.5K. The reticles are usually stored in a reticle storage system, centrally located within the photolithography area, and are cataloged by reticle identification number. The reticle(s) are transported via a conveyor system to the particular stepper(s) in need of a certain reticle. One of the problems with managing reticles is that they are very delicate structures and can be damaged easily by excessive handling. They also need to be routinely inspected to ensure that they are still viable for use in making the intended product.
Cycle times of the photoresist process are limited by the wafer processing system""s limited resources to manage all of the options available on the processing line. Manual intervention is required in managing the finite number of reticles in inventory, the limited number of the duplicate reticles available and the finite number of pods that move the reticles around the photolithography area. Further, midstream changes in production cannot be acted upon as quickly or efficiently due to the lack of centralized management of reticles and reticle storage locations. In view of the above, there is a need for a system and method that will allow for on-demand reticle selection in order to improve cycle time and flexibility on the manufacturing line and for a system that will to reduce the amount of handling of reticles.
The present invention is directed to addressing the above, and other needs in connection with improving efficiencies of reticle stocking and sorting processes.
Semiconductor fabrication facilities have material handling systems that manage production/test wafers as well as empty cassettes and carriers throughout the system. Reticles and reticle storage systems have to be manually integrated with these subsystems and any changes to the reticle flow or storage plan must be manually coordinated by the operators on the line. This has led to delays in the system in processing the wafers and inefficiencies in manufacturing. One aspect of the invention is directed to an automated and integrated reticle management system that reduces delays caused by event changes in the line or management directives external to the line, and that reduces the handling of reticles by having a system that allocates reticles more precisely.
According to another aspect of the invention, a mask stocking and sorting management system is used in a manufacturing facility having a material handling system that presents a mask to a photolithography process area. The system includes an arrangement of pods, each of the pods including at least one mask, and a host system adapted to rearrange the pods at a mask storage location as a function of a mask identification code and an externally provided directive indicating a masking sequence change. In another related embodiment at least one mask sorting apparatus can be coupled to the mask storage system and to the host system to provide more flexibility in the overall mask management system. An important advantage is that the host system reduces the delivery time of a mask to the photolithography area and reduces the number of buffer pods used in the material handling.
According to another aspect of the present invention, a method of stocking and sorting masks is used in a manufacturing facility having a material handling system for presenting a mask to a photolithography process area. An arrangement of pods is provided with each of the pods including at least one mask. The pods are then rearranged at a mask storage location as a function of a mask identification code and an externally provided directive indicating a masking sequence change. An important advantage is that the method reduces the delivery time of a mask to the photolithography area and reduces the number of buffer pods used in the material handling.
In yet another aspect of the present invention, a method of stocking and sorting masks in a manufacturing process involves a photolithography process area and a material handling system. The method includes conducting a status check of all of the masks in the manufacturing process and then preparing a mix of masks within a mask storage system to be transported to the photolithography area via the material handling system. A host system is polled to determine the existence of an instruction change that can change the flow of masks in the manufacturing process. The masks are then used in the photolithography process, are returned to the storage location and the status of the masks are communicated to the host system.
The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures in the detailed description that follow more particularly exemplify these embodiments.